1. Field of the Invention
The present invention relates to a motor control apparatus and a control apparatus for hybrid electric vehicles
2. Description of the Related Art
Automobiles that use a motor as a motive power source to run have been increasing in recent years. These vehicles are environment-responsive automobiles represented by electric automobiles and hybrid vehicles. Some of the major features of these environment-responsive automobiles include using the electric energy of a battery to generate a torque from the motor and thus to actuate tires. For accelerated miniaturization of a power train, an alternating-current (AC) motor such as a permanent-magnet synchronous motor is primarily used as the above driving motor. Additionally, a power inverter is used to supply DC power from the battery to the AC motor, and the DC power from the battery is converted into AC power. The control of this inverter allows variable-speed control of the driving AC motor.
The motor control apparatuses used in these hybrid vehicles have traditionally employed the sine-wave PWM (Pulse Width Modulation) driving scheme in which an AC sine-wave voltage to be applied to the motor is converted into PWM signal form. The sine-wave PWM driving scheme, however, has limits on the voltage utilization ratio of the inverter and is therefore insufficient for providing more powerful driving in the high-speed region of the motor. For this reason, rectangular-wave driving (one-pulse driving) has recently come into use. Rectangular-wave driving only requires on/off control of a voltage pulse, depending upon the plus/minus sign of the voltage command, instead of executing PWM driving in the high-speed region of the motor.
In the rectangular-wave driving scheme, since PWM conversion is not executed and the pulse signal is of such a waveform that the signal is turned on or off, depending upon the plus/minus sign of the AC voltage signal to be applied, the maximum voltage permissible for the inverter to output can be applied to the motor and this motor can be driven in a wider operating range.
As can be understood from the above, to selectively use PWM driving and rectangular-wave driving in different operating regions of the motor, switching from PWM driving to rectangular-wave driving is needed, and the switching operation causes torque pulsations. Accordingly, there is a known technique in which an overmodulation mode for changing continuously the waveform of a voltage signal from the initial sine waveform thereof existing before mode switching, into a rectangular waveform to be obtained after mode switching, is inserted midway between PWM driving and rectangular-wave driving modes to gradually change the signal in amplitude as an AC voltage signal and reduce any torque pulsations occurring during mode switching. JP-A-11-285288, for example, discloses such a technique.